1. Field of the Invention
This invention relates to the preparation of novel thermostable polyesters derived from dihydroxytetraphenylmethane. More particularly, this invention relates to the preparation of such novel thermostable polyesters from dihydroxytetraphenylmethane and a source of an isophthalyl or terephthalyl moiety wherein the polymerization process is conducted in the absence of a catalyst. This invention is also directed to the preparation of highly stable thermopolyesters which can be formed into sheets having good physical properties, especially tensile strength.
2. Discussion of the Prior Art
It has long been known to prepare polyesters by a condensation of a dihydric alcohol and a source of a carboxylic acid. For instance, polyesters are prepared in the condensation of ethylene glycol with a terephthalic acid ester. Generally speaking, a molar excess of dihydric alcohol is employed, and the materials are reacted in a first or precondensation stage to prepare prepolymer which is thereafter reacted in a polycondensation stage to prepare the final polyester. Numerous different carboxylic acids and dihydric alcohols have been proposed as precursors for polyesters.
It has become desirable to provide thermostable polyesters which can be formed into sheets, films, coatings and the like which possess excellent electrical insulating properties. More particularly, it has become desirable to provide a simple and efficient process for the preparation of such polyesters, which process can be conducted without the use of a polycondensation catalyst. Generally speaking, the prior art has advocated the use of polycondensation catalysts in the preparation of polyesters, especially where it is desired to obtain a polyester which is insoluble in certain chlorinated hydrocarbon solvents, e.g. tetrachloroethane.